Methods for scanning an examination object using a CT system are generally known. Circular scannings, sequential circular scannings are used here for example with advance or spiral scannings. With these scannings, absorption data relating to the examination object is recorded from different recording angles with the aid of at least one x-ray source and at least one opposite detector and this thus collected absorption data and/or projections are calculated by means of corresponding reconstruction methods to form sectional images through the examination object.
To reconstruct computed tomography images comprising x-ray CT data records of a computed tomography device (CT device), i.e. of the detected projections, a so-called filtered back projection method (FBP) is nowadays used as a standard method. After the data acquisition, a so-called “rebinning” step is implemented, in which the data generated with the beam propagating in the manner of a fan from the source is rearranged such that it exists in a similar form to that obtained when the detector was struck by x-ray beams running in parallel onto said detector. The data is then transformed into the frequency range. A filtering takes place in the filtering range, and the filtered data is then back-transformed. A back-projection onto the individual voxel within the volume of interest then takes place with the aid of the thus rearranged and filtered data.
As diagnostically relevant information is to be taken from CT images for the patients, a high image quality is extremely important. Because the examination object has been exposed to a radiation dose in order to detect the CT projections, this should not have been “purposeless”. The quality of a CT image depends in particular on the contrast-to-noise ratio. A high contrast enables limits between different materials/tissue types to be able to be clearly identified. It is endeavored to obtain as good a contrast-to-noise ratio of the CT images as possible with the given radiation dose.